The invention relates to a process for preparing 1,n-cyclohexanediamines, where n may have the values 2, 3 and 4. These compounds have the general formula 
where one of the radicals R1 to R3 is an amino group and the two others are hydrogen.
1,n-Cyclohexanediamines, in particular, 1,4-cyclohexanediamine (R3xe2x95x90NH2), are compounds with a variety of potential uses. Of particular interest is their use as building blocks for polymers, for example as an amino component for preparing polyamides, polyimides or polyureas, or as a starting material for preparing diisocyanates for the preparation of polyurethanes. These compounds are, furthermore, bidentate ligands which with various transition metals form complexes of which some are pharmacologically active, for example as cytostatics.
Processes known hitherto for preparing 1,n-cyclohexanediamines are based on the hydrogenation of the corresponding phenylenediamines However, these are relatively expensive, highly toxic and, in particular the para isomer, sensitive to oxidation. There are also processes for the direct hydrogenation of the corresponding nitroanilines, but these are also highly toxic.
The object of the present invention was therefore to provide a process, suitable for carrying out on an industrial scale, and starting from readily obtainable and relatively nonhazardous compounds, for preparing 1,n-cyclohexanediamines.
According to the invention, this object is achieved by the process of the invention.
It has been found that 1,n-cyclohexanediols of the general formula 
where one of the radicals R4 to R6 is a hydroxyl group and the others are hydrogen, can be converted into the desired 1,n-cyclohexanediamines by reacting with ammonia in the presence of hydrogen and of a catalyst based on cobalt, if desired with addition of iron as promoter, in a single-step process at reaction pressures of from 50 to 300 bar and at temperatures of from 100 to 350xc2x0 C. The proportional quantities are usefully 2-200 mol of ammonia and 0.01-20 mol of hydrogen to 1 mole of 1,n-cyclohexanediol. Preference is given to proportional quantities of 10-100 mol, in particular 40-90 mol, of ammonia and 2-10 mol of hydrogen to 1 mole of 1,n-cyclohexanediol.
The reaction pressure is preferably 100-300 bar.
Particular preference is given to pressures of 125-200 bar and to temperatures of 150-230xc2x0 C.
The metal fraction of the catalyst, calculated without any support which may be present, is preferably from 90 to 100 per cent by weight.
Particular preference is given to catalysts which, in addition to the cobalt, comprise from 1 to 60 per cent by weight (based on the total metal content) of iron as promoter. The scope of the invention also includes the use of other promoters, such as rare-earth metals.
The catalysts which may be used according to the invention may, for example, be prepared by precipitating the hydroxides, oxide hydrates and/or hydroxycarbonates of the active metals at pH 5-9, washing the same, drying the same and calcining the same at 200-500xc2x0 C., preferably 300-500xc2x0 C., in an oxidizing atmosphere.
It is advantageous for carrying out the reaction according to the invention if there are basic and acid centres present on the catalyst surface, since adsorption and activation of the ammonia and of the aminoalcohol arising as intermediate can take place at these centres. However, strongly basic or strongly acid centres are disadvantageous, since they reduce the selectivity of the reaction and favour side reactions, such as fragmentation and oligomerization. The pH value during the precipitation affects the acid and/or basic properties of the catalyst. It is therefore essential to carry out the precipitation at a pH of from 5 to 9.
The precipitation may, for example, be brought about by adding a base to a solution of the acetates, nitrates or halides of the metal component(s). Preferred bases are ammonium carbonate and/or ammonium carbamate or ammonia.
The drying preferably takes place at temperatures of up to 150xc2x0 C., if desired in vacuo.
Prior to use the catalyst is advantageously activated in a reducing atmosphere (e.g. hydrogen) at 200-400xc2x0 C. The catalyst in the active form is essentially in metallic form.
The catalyst may have been applied to a support, such as silicon dioxide (e.g. kieselguhr), aluminium oxide or graphite. To this end, the precipitation may take place in the presence of the support.
The novel process is preferably carried out continuously.
The contact time (defined as the quotient calculated from weight of catalyst [g] and molar feed [mol/s] of the reaction partners in the case of continuous operation is preferably 10,000 to 100,000 gxc2x7s/mol.
In the case of continuous conduct of the reaction, the unconverted alcohol and/or the unconverted ammonia is preferably recycled. By this means it is possible to obtain a good product yield even under conditions which during a single pass give only low conversion. The ammonia may be introduced to the reactor as a gas or liquid. The reaction mixture leaving the reactor is advantageously cooled, e.g. by adiabatic expansion, and the ammonia separated off and, if desired, returned to the process.